Vehicle strengthening members may be used to increase load carrying capacity, impact energy absorption, and bending resistance while reducing mass per unit length of the strengthening member.
When a compressive force is exerted longitudinally on a strengthening member (for example, a force due to a front impact load on a vehicle's front rail or other strengthening member in the engine compartment), the strengthening member may crush in a longitudinal direction to absorb the energy of the collision. In addition, when a bending force is exerted on a strengthening member (for example, a force due to a side impact load on a vehicle's front side sill, B-pillar or other strengthening member), the strengthening member may bend to absorb the energy of the collision.
Under axial loading conditions, axial collapse of a strengthening member may proceed in an unstable buckling mode that is initiated in a middle of the strengthening member before moving to a top of the strengthening member in a non-progressive manner. An unstable collapse mode may increase the variation in crash behaviors among replicate samples and may make crash performance more difficult to predict. An unstable collapse mode may also absorb less impact energy and may be less efficient in material utilization compared to a progressive and stable collapse mode.